= a monthly cycle that occurs in women,
involving morphological changes in the _______________ and the
____________________________________ of the uterus, caused by ___________________________________________________
of the hypothalamus, pituitary gland and ovaries

Click herefor diagram of
the hormonal feedback loop between the brain and ovaries.

Length of the cycle is
extremely variable:

Usually ranges from 25 - 30 days, with an average of _______ days.

Cycles <21 days or >35 days are considered
irregular.

Length is more variable in women younger than 20 and older than 40.

Tends to be longer in teenagers (ave. 35
days), becoming gradually shorter with age (30 days at 30 yrs and 28 days
at 35 yrs).

Variation in length may be reduced when sexual intercourse is more
frequent.

Hypothalamus releases hormone GnRH, which signals the pituitary gland to secrete
hormones ______________ and ____________.FSH stimulates
__________________________________ and LH stimulates synthesis of
_______________________________ by the developing follicles. Rising level of
estrogen has a negative feedback on GnRH
secretion, which inhibits further increases in FSH.

By day 13, one dominant (Graffian)
follicle (2 - 2 ½ cm in diameter) is established and the remaining
tertiary follicles degenerate and undergo atresia.

Estrogen level reaches a maximum peak at day 12
or 13, triggering a surge of _____________ from the pituitary
(accompanied by a smaller surge in FSH).

2.Ovulation: the shortest phase; an instantaneous event;
typically occurs on day 14 (of 28 day cycle). Click for diagram.

The surge in LH initiates a resumption of
____________________________ in the oocyte contained within the dominant
follicle and subsequent ______________________________ of the mature egg
(9-12 hours after the peak burst in LH).

Luteal Phase: duration is remarkably consistent among women;
usually about ______________ long. Click
for diagram.

After ovulation, a
______________________________________ is formed inside the ovary from
the remnants of the collapsed follicle that released the egg.

This structure secretes both
_____________________________and ______________________________________,
which together inhibit GnRH secretion from the
hypothalamus.

This, in turn, results in a drop in ___________
(and FSH) levels, thereby preventing a second ovulation from occurring.

The corpus luteum reaches a peak of activity
about 7 - 8 days after ovulation. If the egg was fertilized, the blastocyst implants in the endometrium at that time.

In the absence of fertilization, there are no (hCG) hormones from the
developing embryo to maintain the corpus luteum, so it
_________________________________________ about 10 days after ovulation.
Blood levels of estrogen and progesterone therefore _______________,
resulting in degeneration of the endometrial layer and the onset of
menstruation about 4 days later.

The rapid drop in blood levels of estrogen and
progesterone (due to the degeneration of the corpus luteum in the ovary)
causes the upper 2/3 of the endometrial layer of the uterus to
degenerate. It is then shed from the body.

As the lining degenerates, the underlying blood
vessels bleed, leading to a loss of 1 - 8 oz of blood (ave. 1 - 3 oz) over the menstrual period.

2.Proliferative Phase: proliferation of new cells in uterine lining; duration usually 8 – 10
days

The rising level of estrogen in the bloodstream
(produced by the next crop of growing follicles) promotes rapid
_______________________ and ____________________________ of the uterine
lining within a few days after the end of the menstrual phase.

The new layer proliferates rapidly during the
days before ovulation, but nutrient secretion is minimal during this
time.

Secretory Phase: thickening of the uterine lining after
ovulation; duration is usually 2 wks

Following ovulation, the glands of the
endometrium begin secreting large amounts of
_______________________________ that will be used by the developing
embryo if fertilization and implantation occur.

In preparation for the possibility of
pregnancy, the endometrium becomes twice as thick as it was during the
previous phase, resulting in a thick, nutritive layer, suitable for
implantation. _______________________________ supply
to the endometrium also increases.

oCause is still
_____________________________. Given such a wide variety of symptoms, there is
not likely to be a single cause. Probably multifactorial.
There are two prevailing theories, each with supporting evidence: